Low molecular weight polyphenols and ellagitannins were analyzed by HPLC, and the molecular weight distribution of ellagitannins was calculated by GPC, in oak heartwood of Quercus robur L., Quercus petraea Liebl., Quercus pyrenaica Wild., and Quercus faginea Lam., grown in Spain, before and after 1 year of seasoning, in Bordeaux, France. During this process, the concentrations of low molecular weight polyphenols (acids and aldehydes, benzoic and cinnamic, and coumarins) increased, and those of ellagitannins (castalagin, vescalagin, and roburins A-E) decreased. A similar behavior for the A and B compounds in all species was not found. This modification in the chemical composition was similar in the four Spanish species of Quercus studied and allowed the differentiation between the unseasoned wood and the wood after the first year of seasoning.
Low molecular weight polyphenols were studied by HPLC in samples of cork
from different trees of
Spanish Quercus suber and at different industrial processing
stages. Gallic, protocatechuic, vanillic,
caffeic, ferulic, and ellagic acids; protocatechuic, vanillic,
coniferylic, and sinapic aldehydes, and
aesculetin and scopoletin were identified and quantified. Ellagic
acid was the main component in
all of the samples, followed by the rest of the phenolic acids, which
had very much lower
concentrations. Four components, caffeic, ferulic, and
protocatechuic acids and vanillin, were selected
as those that provided the greatest differences among the trees
studied. In relation to the four
industrial processing stages considered, marked differences were
observed between the first two
stages, stripping and first rest, and the stages after boiling. In
this case, the discriminant variables
were coniferaldehyde, sinapaldehyde, and ellagic acid.
Keywords: Quercus suber; cork; polyphenols; phenolic acids and aldehydes;
coumarins; high-performance liquid chromatography
In this work, a study on tannins (proanthocyanidins and ellagitannins) is carried out in bark extracts from different Eucalyptus species grown in Spain: E. camaldulensis, E. globulus and E. rudis. The tannin analysis was carried out using HPLC and classical chemical methods. Bark extracts were characterized by the abundance of polymeric proanthocyanidins and by the diversity of ellagitannins. The ellagitannins composition was related with the species and the tree provenance, allowing to discriminate E. globulus from E. camaldulensis and E. rudis.
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